The present invention relates to a mixed green-emitting phosphor and a cathode-ray tube using the same, and in more detail, to a mixed green-emitting phosphor for use in a projection cathode-ray tube which has an excellent luminance saturation characteristic under high current density and a cathode-ray tube using the same.
In a green-emitting phosphor for use in a general cathode-ray tube, ZnS-based phosphors, such as ZnS:Cu,Au,Al phosphor, ZnS:Cu,Al phosphor, etc., are generally used.
However, cathode-ray tubes which are operated under high current density and high voltage drive have recently attracted much attention as cathode-ray tubes become large and high-definition. Therefore, a phosphor of high luminance especially under high current density, is needed. However, since the conventional ZnS-based phosphors are unable to provide sufficient luminance effects under high current density, the rare earth phosphors have been used recently.
As examples of rare earth green-emitting phosphors which are activated under high current density, such as in the projection cathode-ray tube, Y.sub.3 (Al,Ga).sub.5 O.sub.12 :Tb phosphor, InBO.sub.3 :Tb phosphor, Y.sub.2 SIO.sub.5 :Tb phosphor, LaOCl:Tb phosphor, Zn.sub.2 SiO.sub.4 :Mn phosphor, or mixtures thereof can be enumerated.
The Y.sub.3 (Al,Ga).sub.5 O.sub.12 :Tb phosphor has good current-luminance saturation characteristics and high emitting luminance.
The Y.sub.2 SiO.sub.5 :Tb phosphor is known as having high color purity, short afterglow time and, especially, good luminance saturation characteristics.
For the LaOCl:Tb phosphor, it has good current-luminance saturation characteristics and high color purity.
Zn.sub.2 SiO.sub.4 :Mn phosphor is known as not having good luminance saturation and afterglow characteristics, but having excellent color purity.
The InBO.sub.3 :Tb phosphor has a high resistance under high current density, is suitable for use in the projection cathode-ray tube, and has good color purity. Meanwhile, the afterglow time is long so as to mix with the phosphor whose afterglow time is short when applied to a cathode-ray tube.
There are many mixed green-emitting phosphors prepared by mixing the above-mentioned rare earth-based phosphors. As one example, U.S. Pat. No. 4,924,139 discloses a mixed phosphor of InBO.sub.3 :Tb with Y.sub.3 (Al,Ga).sub.5 O.sub.12 :Tb whose color purity is excellent and whose afterglow time is short.
However, the above mentioned phosphors and the mixed phosphors thereof have undesirable luminance saturation and deterioration characteristics. Accordingly, there are many problems that should be improved in the known phosphors.